Storage systems incorporate some form of protection against data loss. One form of protection against data loss is redundant data storage, for example redundant array of independent disks (RAID) schemes. If the physical bits stored on a single disk are lost, the surviving physical bits on other disks either contain a copy of the lost data or are sufficient for a mathematical recalculation of the lost data. Thus, the data stored by the system has not been lost even when some physical bits have been lost. Loss of data may occur if enough physical bits are lost so as to exceed the degree of protection provided by the redundant data storage.
When some data loss has been experienced, the impact of the loss on the data owner depends on which parts of the data have not been lost. Some distributions of the data loss cause greater harm to the data owner than others, and it is an objective in the system to keep that harm small. Another objective is to maximize the performance that is offered for storage and retrieval of data both in the absence of any data loss event and subsequent to a data loss event.